The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft is moved by several turbojet engines each housed in a nacelle also accommodating a set of annex actuating devices pertaining to its operation and providing diverse functions when the turbojet engine is in operation or stopped.
A nacelle generally exhibits a tubular structure comprising an air inlet upstream of the turbojet engine, a median section intended to surround a fan of the turbojet engine, a downstream section accommodating thrust reversal means and intended to surround the combustion chamber of the turbojet engine, and is generally terminated by an ejection nozzle of which the outlet is located downstream of the turbojet engine.
Modern nacelles are intended to accommodate a double flow turbojet engine able to generate by means of the blades of the fan in rotation a hot air flow (also called primary flow) from the combustion chamber of the turbojet engine, and a cold air flow (secondary flow) which circulates outside the turbojet engine through an annular passage, also called stream, formed between a fairing of the turbojet engine and an inner wall of the nacelle.
The two air flows are ejected from the turbojet engine by the rear of the nacelle.
The role of a thrust reverser is, during the landing of an aircraft, to improve the braking capacity of the latter by redirecting towards the front at least part of the thrust generated by the turbojet engine.
In this phase, the reverser obstructs the stream of the cold air and directs the latter towards the front of the nacelle, thereby generating a counter thrust which is added to the braking of the wheels of the airplane.
The means implemented to achieve this reorientation of the cold flow vary according to the type of reverser.
It may, in particular, be mentioned thrust reversers with gates typically comprising, a thrust reversal cowl associated with gates for diverting the flow uncovered by thrust reversal shutters displaceable by a cowl movement.
Apart from its thrust reversal function, the moveable cowl belongs to the rear section and exhibits a downstream side forming an ejection nozzle for channeling the ejection of the air flows.
This nozzle may come as a complement to a primary nozzle channeling the hot flow and is thus called secondary nozzle.
This nozzle may be moveable with respect to the nacelle in such a manner as to adjust the section for ejecting the stream of cold air flow, according to the position of said nozzle.
The moveable nozzle is also called moveable structure for adjusting the outlet section of the stream.
The optimal section of the nozzle may be adapted according to the different flight phases, namely the take-off, climb, cruise, descent and landing phases of the aircraft.
It is associated with an actuating system allowing to optimize and make its section vary, according to the flight phase in which the aircraft is in.
There are several solutions for achieving the section variation of the nozzle, according to the nacelle form to consider and the provided actuating systems.
Thus, the moveable nozzle may be driven in translation along a substantially longitudinal direction of the nacelle or by pivoting around an axis perpendicular to the longitudinal axis of the nacelle, by a dedicated actuator or not and independently or not from a partial translation of the thrust reverser cowl.
Such displacements of the nozzle according to the different flight phases require methods for controlling the position of the nozzle, that is to say methods for controlling actuators associated with the displacements of the nozzle.
It is thus known, control methods and associated control systems allowing to discretely vary, between different predetermined positions, the position of the nozzle during the different flight phases.
In this context, in as far as the different predetermined positions of the nozzle are spaced apart, the fuel consumption is excessive and the operation of the motor is not optimal.
Moreover, if it is provided to define closer positions for the nozzle, the passages from one position to the other become frequent, thus causing the wear of the control system and the actuating means and as a result, their reliability.
Hence, in a cruise phase of the aircraft, it is provided predetermined positions for the nozzle which are not often suited to the altitude at which the aircraft is flying, this altitude able to be modified during cruise by lightening the aircraft following a decrease in fuel reserves.
In order to optimize the operation of the motor, it is further known, control methods and associated control and actuating systems allowing to continuously, vary, the position of the nozzle during the different phases of flight.
However, this implies a permanent operation of the control system and the associated actuators for placing the nozzle in a determined position, thereby always highly affecting the reliability of these elements with the progression of the flight cycles.